The shoulder is the most flexible joint in the body, allowing for full rotation and a great range of motion. This mobility, however, leaves the shoulder highly susceptible to injury and resulting instability.

Approximately 1% to 2% of people will suffer a shoulder dislocation in their lifetime and young athletes are at a particularly high risk of shoulder instability events – 95% of which occur in the anterior direction.

When a shoulder dislocates, it becomes more vulnerable to future dislocations. In addition to dislocations, other conditions – such as subluxation and hyperlaxity – can lead to shoulder instability.

Shoulder Anatomy

The shoulder is a complex joint of four smaller joints made up of three bones (humerus, scapula and clavicle), connective tissue (ligament system called the shoulder capsule), muscles, tendons, nerves and blood vessels. In the glenohumeral joint of the shoulder, the head of the humerus (upper arm) fits into a shallow socket in the shoulder blade called the glenoid.

The shoulder capsule works to keep the head of the humerus in the center of the glenoid socket and attaches the upper part of the humerus to the scapula (shoulder blade). In this ball-and-socket joint, the ball (head) of the humerus is three to four times bigger than the glenoid socket. While this allows for greater movement of the shoulder joint, it also leaves the glenohumeral joint prone to dislocation.

The labrum, rotator cuff and other muscles and tendons in the shoulder joint also work to stabilize the joint. Dislocations, labrum tears, rotator cuff tears and other shoulder injuries can all lead to chronic shoulder instability.

Types of Shoulder Instability

There are three general types of shoulder instability.

Anterior Shoulder Instability

The most common type of shoulder instability, anterior shoulder instability, typically occurs when the shoulder is in abduction and external rotation. Abduction is when you raise your arm laterally away from your body (think making a “T” with your arms) and external rotation is when you rotate your elbows forward. A good example of a shoulder in abduction and external rotation is when you throw a ball.  

Posterior Shoulder Instability

Posterior instability is much less common than anterior instability and typically stems from muscle contractions (versus trauma in athletes) like those from seizures or severe electric shock. In a posterior dislocation, the head of the humerus is dislocated from the posterior labrum and the glenoid socket.

Multidirectional Shoulder Instability

Unlike anterior and posterior shoulder instability, multidirectional shoulder instability is not a result of dislocation or injury. This type of instability is caused by a congenital hyperlaxity of the glenohumeral joint capsule (naturally looser ligaments in the shoulder) or laxity as a result of repetitive overhead motions (from sports, occupations, etc.).

Someone with congenital hyperlaxity or developed laxity is particularly susceptible to chronic multidirectional instability after a rotator cuff injury or tear.

Shoulder Instability Symptoms

The three different types of shoulder instabilities have a variety of symptoms; consult an orthopedic shoulder specialist for an accurate diagnosis of your symptoms.

Shoulder instability symptoms include:

• Hearing or feeling a “pop” in the shoulder
• Significant pain and discomfort
• Inability to move the shoulder or feel that the shoulder is “stuck”
• Feeling of increased movement in the glenoid socket
• Difficulty lifting the arm overhead
• Weakness in the shoulder and/or arm

Chronic shoulder instability symptoms include:

• Repeated instances of the shoulder “giving out” or getting “stuck”
• Repeated shoulder dislocations
• Ongoing sensation of the shoulder slipping in and out of the glenoid socket or feeling loose
• Feeling like the shoulder is “dead” or just hanging there

Shoulder Instability Tests

There are a number of tests your orthopedic shoulder surgeon will conduct to diagnose shoulder instability, including the load-and-shift maneuver, the relocation test, the drawer test, the sulcus test and the anterior apprehension test.

During these tests, your doctor will manipulate your joint and ask you to move your arm and shoulder in specific ways to evaluate your shoulder injury. If necessary, your orthopedic specialist will order X-rays to look for any bone injuries in your joint or an MRI to see if you have any additional ligament or tendon damage.

Shoulder Instability Treatment

Closed Reduction

If you have suffered an anterior or posterior dislocation, your orthopedic surgeon will first try a closed reduction – meaning they will try to physically set your shoulder joint back into place. If this is possible, any severe pain should resolve almost immediately. If a closed reduction doesn’t work, surgery may be necessary.

Surgery

If you have had recurring shoulder dislocations, a weak shoulder or torn ligaments, surgery may be necessary. While rare, surgery is also necessary if you have damaged nerves or blood vessels in your shoulder joint.

Immobilization

Whether your shoulder injury requires a closed reduction, surgery or neither, your doctor most likely will immobilize your shoulder with a splint or sling to keep the joint in place.

Shoulder Instability Exercises

Your doctor may prescribe physical therapy to help strengthen your shoulder muscles to improve stability in and around the joint. Your physical therapist will often provide a program of shoulder instability exercises for you to do at home, as well.  

If you’re suffering from shoulder instability or have experienced a dislocation, please see an orthopedic specialist for treatment. If you have any questions about shoulder instability, symptoms or treatments, please contact us or leave a comment below.